Mixtures of cyclic branched siloxanes of the D/T type and conversion products thereof

ABSTRACT

Mixtures of cyclic branched siloxanes having exclusively D and T units and having no functional groups, with the proviso that the cumulative proportion of the D and T units having Si-alkoxy and/or SiOH groups that are present in the siloxane matrix, determinable by 29Si NMR spectroscopy, is ≤2 mole percent, are described, as are branched organo-modified siloxanes obtainable therefrom.

RELATED APPLICATION

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 15/719,775, entitled “MIXTURES OF CYCLIC BRANCHEDSILOXANES OF THE D/T TYPE AND CONVERSION PRODUCTS THEREOF” filed on Sep.29, 2017, the application of which is related and incorporates byreference European Patent Application Serial No. 17156421.4 filed Feb.16, 2017, and European Patent Application No. 16198809.2 filed Nov. 15,2016, the disclosures of which are expressly incorporated herein byreference.

The invention relates to a process for preparing mixtures of cyclicbranched siloxanes of the D/T type, to the mixtures of cyclic branchedsiloxanes of the D/T type themselves, and to the processing of thesesiloxanes to give functionalized branched siloxanes and/or branchedsiloxanes.

Cited as a reference in relation to the M, D, T, Q nomenclature used inthe context of this document to describe the structural units oforganopolysiloxanes is W. Noll, Chemie and Technologie der Silicone[Chemistry and Technology of the Silicones], Verlag Chemie GmbH,Weinheim (1960), page 2 ff.

In the preparation of organomodified siloxanes, especially branchedfunction-bearing siloxanes, a difficulty frequently encountered is thatcompeting processes that take place simultaneously in the reactionmatrix can adversely affect the quality of the desired product.

Condensation and equilibration are among these competing processes,which have to be considered separately according to the syntheticproblem. A great challenge is the homogeneous distribution of branchingsites along a siloxane chain, corresponding to avoidance of T-structureddomains. As can be inferred from the literature, the breakup ofhomologous siloxane chains consisting of T units under acid catalysis inparticular is difficult and hence in effect cannot be accomplished inthe presence of sensitive functional groups. With regard to thereactivity characteristics of M, D and T units, reference is made to M.A. Brook, “Silicon in Organic, Organometallic and Polymer Chemistry”,John Wiley & Sons, Inc., New York (2000), p. 264 ff.

Especially in the preparation of branched siloxanes bearing reactive SiHgroups, considerable efforts are therefore always made to reconcile thedemand for uniform distribution of siloxane units as far as possible ina statistical manner with the demand for very substantial retention ofthe valuable silicon-bonded hydrogen.

Polyorganosiloxanes are prepared according to prior art by hydrolysisand condensation proceeding from methylchlorohydrosilanes having mixedsubstitution. Direct hydrolytic condensation of hydrogen-containingsilanes, for example dimethylmonochlorosilane or methyldichlorosilane,is described, for example, in U.S. Pat. No. 2,758,124. In this case, thesiloxane phase that separates in the hydrolysis is separated from thewater phase having a hydrochloric acid content. Since this process isprone to gelation of the hydrosiloxanes, DE 11 25 180 describes animproved process utilizing an organic auxiliary phase, in which thehydrosiloxane formed is present as a separate phase dissolved in anorganic solvent and, after separation from the acidic water phase anddistillative removal of the solvent, is resistant to gelation. A furtherprocess improvement with regard to minimized solvent input is describedby EP 0 967 236, the teaching of which involves first using only smallamounts of water in the hydrolytic condensation of theorganochlorosilanes, such that hydrogen chloride is driven out ingaseous form in the first step and can be sent directly to further enduses as a material of value.

Branched organomodified polysiloxanes can be described by a multitude ofstructures. In general, a distinction has to be made between a branch orcrosslink which is introduced via the organic substituents and a branchor crosslink within the silicone chain. Organic crosslinkers forformation of siloxane skeletons bearing SiH groups are, for example,α,ω-unsaturated diolefins, divinyl compounds or diallyl compounds, asdescribed, for example, in U.S. Pat. No. 6,730,749 or EP 0 381 318. Thiscrosslinking by platinum-catalysed hydrosilylation downstream of theequilibration means an additional process step in which bothintramolecular linkages and intermolecular linkages can take place. Theproduct properties are additionally greatly affected by the differentreactivities of the low molecular weight organic difunctional compoundsthat have a tendency to peroxide formation.

Multiple crosslinking of the silicone block of an organomodifiedpolysiloxane with the organic block copolymer can be effected in variousways. EP 0 675 151 describes the preparation of a polyethersiloxane byhydrosilylation of a hydrosiloxane with a deficiency ofhydroxyfunctional allyl polyether, in which unconverted SiH functionsare joined to the hydroxyl groups of the polyether substituents via anSiOC bond with addition of sodium methoxide. The increase in molar massleads to broad scatter in the product properties, for example theviscosity. A similar approach to the formation of branched systems isdescribed by U.S. Pat. No. 4,631,208, in which hydroxy-functionalpolyethersiloxanes are crosslinked by means of trialkoxysilanes. Bothmethods lead to intermolecular crosslinking of the polyethersiloxaneswhere it is not only difficult to control the increase in molar mass butwhere there are also associated unpredictable rises in viscosity.Following the aforementioned methods, what is obtained is not branchingwithin the siloxane portion at constant molar mass, but crosslinking togive macromolecular multiblock copolymers.

Branching within the siloxane chain therefore already has to be effectedin the course of production of the hydrosiloxane, in order to get roundthe described disadvantages of the crosslinking. Branches within thesiloxane chain require the synthetic incorporation of trifunctionalsilanes, for example trichlorosilanes or trialkoxysilanes.

As known to the person skilled in the art, the rate of hydrolysis of theorganochlorosilanes rises in the following series (C. Eabom,Organosilicon Compounds, Butterworths Scientific Publications, London1960, p. 179):SiCl₄>RSiCl₃>>R₂SiCl₂>R₃SiCl.

Therefore, in the hydrolysis and condensation reactions oftrichlorosilanes, there is an elevated tendency to formation of highlycrosslinked gels compared to the slower hydrolysis and condensationreactions of difunctional and monofunctional organochlorosilanes. Theestablished processes for hydrolysis and condensation of dichloro- andmonochlorosilanes are therefore not directly applicable totrichlorosilanes; instead, it is necessary to take indirect routes viamultistage processes.

Building on this finding, it is also necessary to conduct thepreparation of singly branched hydrosiloxanes by incorporation of notmore than one trifunctional monomer per siloxane chain in a two-stageprocess according to the prior art. In a first step, a trifunctional lowmolecular weight hydrosiloxane is prepared by hydrolysis andcondensation from 1,1,3,3-tetramethyldisiloxane andmethyltriethoxysilane, as taught, for example, by DE 37 16 372. Only ina second step is equilibration then possible with cyclic siloxanes togive higher molar masses, as explained by DE 10 2005 004676. For furtherconversion- and therefore only in a third step—the singly branchedhydrosiloxane thus prepared can be provided by the methods known per sefor functionalization of siloxane compounds having SiH groups withorganic substituents.

For synthesis of multiply branched hydrosiloxanes which, by definition,have more than one trifunctional monomer per siloxane chain, there arelikewise two-stage syntheses in the prior art. In principle, it ispossible to proceed from hydrosiloxanes and to subject the SiHfunctions, with addition of water and precious metal catalyst, todehydrogenative conversion to silanols which are then condensed in turnwith hydrosiloxanes. This procedure is described in U.S. Pat. No.6,790,451 and in EP 1 717 260. Quite apart from the costs of theprecious metal catalysis, the poor storage stability of the silanols,which have a tendency to autocondensation, makes it difficult toaccomplish a reproducible, controlled process regime.

A further option described in U.S. Pat. No. 6,790,451 is that ofpreparing a copolymer from trichloromethylsilane ortrialkoxymethylsilane with hexamethyldisiloxane ortrimethylchlorosilane, also called MT polymer therein, which isequilibrated in a second step together with apolydimethyl(methylhydro)siloxane copolymer. The preparation of such MTpolymers entails the use of strong bases or strong acids, in some casesin combination with high reaction temperatures, and results inprepolymers of such high viscosity that the neutralization thereof ismade considerably more difficult and hence further processing to giveend products of constant composition and quality is significantlylimited.

According to EP 0 675 151, first of all, the hydrolysis and condensationof the SiH-free branched silicone polymer is conducted in xylene in sucha way that the final occlusion of the precondensate is conducted with alarge excess of hexamethyldisiloxane and, in the second step, theequilibration is undertaken with methylhydropolysiloxane to give abranched hydrosiloxane (preparation method 6, ibid.). As an alternative,the teaching of EP 0 675 151 relates to a procedure for preparation ofnon-SiR-functional branched siloxanes including merely a partialcondensation of the methyltrichlorosilane used (preparation method 7,ibid.). However, these two strategies do not address the need for auniversally utilizable preparation method for branched siloxanes.

W02009065644 (A1) teaches a process for preparing branchedSiR-functional siloxanes by reacting a mixture comprising a) one or moreSiR-functional siloxanes, b) one or more SiH function-free siloxanes andc) one or more trialkoxysilanes with addition of water and in thepresence of at least one Bronsted-acidic catalyst, wherein the reactionis conducted in one process step. The technical limits of this processbecome clear from the disclosure therein with regard to the conservationof the SiH functionality introduced into the system. This shows the needto work with at least two acidic catalysts (trifluoromethanesulfonicacid vs. trifluoromethanesulfonic acid and sulfuric acid ion exchangeresin, ibid. examples 5 and 6) for sensitive SiR-functional branchedsiloxane structures, which makes the process extremely inconvenient andcostly in terms of its industrial implementation.

There has already been speculation in the literature about the possibleexistence of siloxanes formed exclusively from D and T units. As statedby W. Noll in Chemie and Technologie der Silicone, Weinheim (1960),pages 181-182, D. W. Scott (J. Am. Chem. Soc. 68, 356, 1946) was thefirst to suggest that bicyclic compounds of siloxanes having D and Tunits derive from an extremely dilute co-hydrolysis ofdimethyldichlorosilane and methyltrichlorosilane with subsequent thermalrearrangement. It was possible to isolate isomers in amounts of not even1% from the viscous co-hydrolysate at bottom temperatures between 350and 600° C., and they were then described by cryoscopic and elementalanalysis with very high levels of uncertainty. Scott speculates that hiscompounds having D-T structures contain T structural elements joineddirectly to one another and not via D units. The interpretation of theresults in Scott is based on the premise that all the SiC bonds presentin the cohydrolysate withstand the severe thermal treatment that hechose.

Makarova etal. (Polyhedron Vol. 2, No.4, 257-260 (1983)) prepared 10oligomeric methylsiloxanes having cyclic and linear segments by thecontrolled low-temperature condensation of siloxanes having SiOH groupsand containing SiC! groups in the presence of organic amines such astriethylamine or aniline in benzene or diethyl ether as solvents,separated off the precipitated amine hydrochlorides, and washed and thenfractionally distilled the crude reaction products. Subsequently, thebicyclic methylsiloxanes were subjected to pyrolysis at temperaturesbetween 400 and 600° C., and the pyrolysis products were characterizedby gas chromatography. The low molecular weight compounds used in thecourse of this study, for example hydroxynonamethylcyclopentasiloxane,hydroxyheptamethylcyclotetrasiloxane, dihydroxytetramethyldisiloxane,from the point of view of the silicone chemistry conducted on theindustrial scale, are considered to be exotic species of purely academicinterest.

More particularly, the pure-chain siloxane compounds of the D/T typedefined in terms of molar mass that have been synthesized by this routeare unsuitable for the production of organomodified siloxanes that areemployed in demanding industrial applications, for example in PU foamstabilization or in the defoaming of plastics, etc. Active ingredientsthat effectively address such a field of use are always characterized bya broad oligomer distribution comprising high, moderate and low molarmasses, since the oligomers present therein, depending on their molarmass and hence their diffusion characteristics, are very commonlyimputed to have differentiated surfactant tasks in different timewindows of the respective process. Specifically in the case of thebranched organomodified siloxanes, due to the reaction characteristicsof M, D and T units that have been discussed at the outset, however, agood oligomer distribution combined with a uniform distribution ofsiloxane units in a statistical manner as far as possible in theindividual molecules can only be achieved when the starting material ofthe D/T type used already itself conforms to a distribution function.This is all the more true when the organomodification is effected via anintermediate bearing SiH groups.

Acknowledging this prior art, there is no apparent real solution forpreparation of branched organomodified siloxanes.

It has now been found that, astonishingly, the problem outlined can besolved by conducting the preparation process for obtaining branchedorganomodified siloxanes in such a way that in a first step thepreparation of mixtures of cyclic branched siloxanes having exclusivelyD and T units and having essentially no functional groups is conducted,where a trialkoxysilane in a solvent is reacted with siloxane cyclesand/or, preferably or, α,ω-dihydroxypolydimethylsiloxane with additionof water and in the presence of at least one acidic catalyst, especiallywith the proviso that the cumulative proportion of the D and T units,the Si-alkoxy and SiOH groups respectively, present in the siloxanematrix, determinable by ²⁹Si NMR spectroscopy, is not more than 2 molepercent, and

in a second step the cyclic branched siloxanes are subjected to acidicequilibration with silanes and/or siloxanes, especially with functionalsilanes and/or siloxanes.

This gives rise to the following items of subject matter of theinvention.

The invention provides mixtures of cyclic branched siloxanes havingexclusively D and T units and having no functional groups, with theproviso that the cumulative proportion of the D and T units havingSi-alkoxy and/or SiOH groups that are present in the siloxane matrix,determinable by ²⁹Si NMR spectroscopy, is ≤2 mole percent, otherwisehaving no functional groups.

The invention further provides processes for preparing mixtures ofcyclic branched siloxanes having exclusively D and T units and havingessentially no functional groups, especially mixtures of cyclic branchedsiloxanes having exclusively D and T units, with the proviso that thecumulative proportion of the D and T units having Si-alkoxy and/or SiOHgroups present in the siloxane matrix, determinable by ²⁹Si NMRspectroscopy, is ≤2 mole percent, otherwise having no functional groups,wherein a trialkoxysilane in a solvent is reacted with siloxane cyclesand/or, preferably or, α,ω-dihydroxypolydimethylsiloxane, with additionof water and in the presence of at least one acidic catalyst.

The invention still further provides a process for preparing branchedorganomodified siloxanes, wherein a first step cyclic branched siloxanesare provided, preferably mixtures of cyclic branched siloxanes havingexclusively D and T units and having no functional groups, with theproviso that the cumulative proportion of the D and T units havingSi-alkoxy and/or SiOH groups that are present in the siloxane matrix,determinable by ²⁹Si NMR spectroscopy, is ≤2 mole percent, otherwisehaving no functional groups, in a second step the cyclic branchedsiloxanes are equilibrated under acidic conditions with silanes and/orsiloxanes.

The invention and its subject matter are more particularly elucidatedhereinafter.

In the inventive mixtures of cyclic branched siloxanes havingexclusively D and T units, in a preferred embodiment of the invention,the ratio of D to T units is between 10:1 and 3:1, preferably between6:1 and 4:1.

In a further preferred embodiment of the invention, the molar mass ratioM_(w)M_(n) of the mixture is in the range of 2<M_(w)/M_(n)<50. Theseparameters can be determined from toluenic solutions of the siloxanes bygel permeation chromatography (GPC), which, with utilization of arefractive index detector, by comparison with a polystyrene standard,permits the determination of the mean molar mass M_(w) thereof and themolar mass distribution M_(w)Mn thereof.

When the mixtures of cyclic branched siloxanes having exclusively D andT units, as described above, have the feature that the branching T unitderives from alkyltrialkoxysilanes and/or, preferably or,phenyltrialkoxysilanes, this is a further preferred embodiment of theinvention.

A preferred embodiment of the invention is likewise when the branching Tunit derives from methyltriethoxysilane.

The aforementioned mixtures according to the invention can especially beobtained via the process according to the invention for preparingmixtures of cyclic branched siloxanes having exclusively D and T units,by reacting a trialkoxysilane in a solvent with siloxane cycles and/or,preferably or, α,ω-dihydroxypolydimethylsiloxane, with addition of waterand in the presence of at least one acidic catalyst. This compriseshydrolysis and condensation under acid-equilibrating conditions.

There follows a more particular description of a procedure which ispreferred but nevertheless is merely an example and therefore does notrestrict the subject-matter of the invention:

Preferably, trialkoxysilane and siloxane cycles can be initially chargedin a suitable solvent (for example toluene or cyclohexane), and acatalytic amount of an equilibrating acid (e.g. 0.2 m % oftrifluoromethanesulfonic acid, based on the mass of the reactantswithout solvent) can be added.

Preliminary equilibration is effected, for example, in toluenic phase at60° C. for 4 hours, then a water/ethanol mixture (100% excess of H₂Obased on the groups to be condensed) is added and the reaction mixtureis heated, for example to reflux temperature (about 80° C.) for 4 hours.The reflux condenser is preferably replaced by a water separator and thereaction mixture is heated to about 100° C. within one hour, in thecourse of which the bottom temperature rises constantly with progressivedischarge of the volatiles. When the excess water has been separated outcompletely, the reaction mixture becomes clear.

After cooling to about 70° C., for example, a second portion of awater/ethanol mixture (about ⅓ of the amount used in the preliminaryequilibration step) is added and the reaction mixture is heated toreflux temperature (about 80° C.) for 1 hour. The reflux condenser isreplaced by a water separator and the reaction mixture is heated toabout 100° C. The bottom temperature rises with progressive discharge ofthe volatiles. At the juncture when the excess water has been separatedout completely, the reaction mixture becomes clear.

The reaction mixture is cooled to about 60° C. and, for the purpose ofneutralization, 4 m % of NaHCO₃ is added while stirring. After about 30minutes, the reaction mixture is freed of the solids by filtration. Thesolvent (toluene) is distilled off at 70° C. and an applied auxiliaryvacuum of 1 mbar.

What are obtained are clear colorless liquids of low viscosity, thecorresponding ²⁹Si NMR spectrum of which demonstrates the dominatingpresence of D and T units. The ratio of D to T units is preferablybetween 10:1 and 3:1, preferably between 6:1 and 4:1. By spectroscopy,Si-alkoxy and SiOH groups are found with signal intensities of about0.5% to 1% at most, if at all. The determinable cumulative proportion ofthe D and T units having Si-alkoxy and SiOH groups present in thesiloxane matrix is in any case ≤2 mole percent.

The aforementioned illustrative procedure leads to excellent resultswith a view to the aim to be achieved in accordance with the invention.

If, in the process according to the invention, the solvent used is aninert water-immiscible silicon-free solvent, preferably from the groupcomprising the isomeric xylenes, alkylaromatics such as preferablytoluene and/or cycloaliphatics such as preferably cyclohexane, or elseethyl carbonate, advantageously in mass ratios of solvent to thesiloxane of 1:1 to 5:1, this is a preferred embodiment of the invention.

Depending on the desired D/T ratio, the amount of solvent is preferablysuch as to assure viscosities that can be handled in an efficient mannerover the course of the reaction. Preferably, mass ratios of solvent tothe siloxane of 1:1 to 5:1 are chosen. Particularly in the case of D/Tratios less than 5:1, an unadjusted amount of solvent can lead to risesin viscosity extending as far as gelation. On the other hand, a fewpreliminary tests (see Example 4 (gelated system) and Example 5(manageable system)), once the solvent has been chosen, can be used tofix the optimal mass ratio of solvent to the siloxane.

The acidic catalyst used in the process according to the invention, in apreferred embodiment of the invention, may be (a) para-toluenesulfonicacid, trifluoromethanesulfonic acid, trichloroacetic acid, sulfuricacid, perchloric acid, phosphoric acid and/or hexafluorophosphoric acid,preferably in amounts of 0.1 to 2.0 percent by weight, more preferablyin amounts of 0.15 to 1.0 percent by weight, based in each case on thesilicon-containing component of the reaction matrix,

or

(b) a macrocrosslinked ion exchange resin containing sulfonic acidgroups, preferably in amounts of 1.0 to 10.0 percent by weight, morepreferably in amounts of 2.0 to 6.0 percent by weight, based in eachcase on the silicon-containing component of the reaction matrix.

Suitable acidic catalysts are described in more detail hereinafter.

If the reaction is conducted at temperatures in the range from 10° C. to150° C., preferably 20° C. to 120° C., especially for 40° C. to 110° C.,this is a further preferred embodiment of the invention.

If an at least 100% H₂O excess based on the groups to be condensed isused, this is likewise a further preferred embodiment of the invention.

If the reaction comprises a preliminary equilibration step attemperatures of T>40° C., followed by a condensation initiated byaddition of water at temperatures of T>60° C., where the water is addedin one portion, in several portions or continuously, this is again afurther-preferred embodiment of the invention.

As already set out in detail further up, the invention further providesa process for preparing branched organamodified siloxanes, wherein, in afirst step, cyclic branched siloxanes are provided, preferably mixturesof cyclic branched siloxanes having exclusively D and T units and havingno functional groups, with the proviso that the cumulative proportion ofthe D and T units having Si-alkoxy and/or SiOH groups that are presentin the siloxane matrix, determinable by ²⁹Si NMR spectroscopy, is notmore than 2 mole percent, otherwise having no functional groups, and ina second step the cyclic branched siloxanes are subjected to acidicequilibration with silanes and/or siloxanes, preferably functionalsilane and/or siloxane.

Functional silane and/or siloxane are understood to mean all thosecompounds comprising one silicon atom and/or multiple silicon atomswhich can be incorporated into the copolymer (corresponding to cyclicbranched siloxanes) by way of acidic equilibration. More particularly,these acid-equilibratable silanes or siloxanes, as well as any hydrogen,alkyl or aryl, or vinyl substituents present, also have hydroxyl, alkoxyand chlorine substituents. Likewise suitable here are functional silanesor siloxanes that bear acidic moieties such as toluenesulfonate,trifluoromethylsulfonate and sulfate radicals.

As a special case, branched silicone oils are obtainable by the acidicco-equilibration of the cyclic branched siloxane of the D/T typeobtained in the first step with hexamethyldisiloxane and/or, preferablyor, polydimethylsiloxanes. A corresponding process according to theinvention for preparing branched silicone oils, wherein in a first stepmixtures of cyclic branched siloxanes are provided, as described above,and in a second step the mixtures of cyclic branched siloxanes arereacted with polydimethylsiloxanes or hexamethyldisiloxane, thuscorresponds to a further part of the subject-matter of the invention.

However, it is more preferable in accordance with the invention toprovide branched organomodified siloxanes. For achievement of such afinal organomodified siloxane structure, an acidic equilibration withfunctional silanes and/or siloxanes is conducted as the second step.

Suitable acidic catalysts for both steps of the process according to theinvention are the strong acids (equilibrating acids) known from theprior art for siloxanes, i.e. mineral acids, for example sulfuric acid,but also sulfonic acids, fluoroalkylsulfonic acids, for exampletrifluoromethanesulfonic acid, acidic aluminas or acidic ion exchangeresins, for example the products known by the Amberlite®, Amberlyst® orDowex® and Lewatit® brand names.

In the process according to the invention, it is possible to use eithernatural ion exchangers, for example zeolites, montmorillonites,attapulgites, bentonites and other aluminosilicates, or synthetic ionexchangers. The latter are preferably solids (usually in granular form)with a threedimensional, water-insoluble, high molecular weight matrixbased on phenol-formaldehyde resins or copolymers ofstyrene-divinylbenzene into which numerous “anchor groups” of differentacidity have been incorporated.

Acidic ion exchangers used advantageously in the context of the presentinvention include those as described in EP 1 439 200.

Preference is given to using sulfonic acid catalysts and very particularpreference to using trifluoromethanesulfonic acid.

In the first step of the process according to the invention(corresponding to the preparation of the mixtures of cyclic branchedsiloxanes as described above), it is possible in principle to use anytrialkoxysilanes. Trialkoxysilanes used may be those in which the alkoxyradicals are all the same or all different or in which some are thesame. Trialkoxysilanes used may especially be triethoxysilanes,preferably methyltriethoxysilane, alkyltriethoxysilanes, for examplen-propyltriethoxysilane, isobutyltriethoxysilane, pentyltriethoxysilane,hexyltriethoxysilane, octyltriethoxysilane, hexadecyltriethoxysilane,n-octadecyltriethoxysilane, halogenated or pseudohalogenatedalkyltrialkoxysilanes, especially alkyltriethoxysilanes, for examplechloropropyltriethoxysilane,tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane,nonafluoro-1,1,2,2-tetrahydrohexy ltriethoxysilane, 3-cyanopropyltriethoxysilane, trialkoxysilanes, especially triethoxysilanes havingfunctional groups, for example 3-methacryloyloxypropyltriethoxysilane,3-mercaptopropyltriethoxysilane, 5-(bicycloheptenyl) triethoxysilane,phenyltriethoxysilane, (p-chloromethyl) phenyltriethoxysilane,N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole ordihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione. It may beadvantageous for organically functionalized trialkoxysilanes to be usedas branching unit (included in the equilibration).

Suitable compounds for functionalization of these cyclic branchedsiloxanes, as described in detail further up, in the second step are inprinciple all acid-equilibratable silicon compounds, preferably silanesand/or siloxanes, which can be used for acidic equilibration.

The silanes and/or siloxanes used are any acidequilibratable siliconcompounds, the silanes used especially being diethoxydimethylsilane,trimethylalkoxysilane and dimethyldichlorosilane, and the siloxanes usedespecially being tetramethyldisiloxane,α,ω-dihydropolydimethylsiloxanes, poly(methylhydro)siloxanes,α,ω-dialkoxypolydimethylsiloxanes or α,ω-divinylpolydimethylsiloxanes.

A crucial advantage of the preparation process according to theinvention is that the synthesis of mixtures of cyclic branched siloxaneswithout functional groups, which is the aim in the first step, can beconducted under severe reaction conditions, for example at a high acidconcentration and high temperatures, without product damage since thereare no sensitive moieties present at all (for example SiH functions).Optimal incorporation of branching units (T structures) into themolecular skeletons of the siloxane oligomers is thus possible, wherethe T structures are ideally separated by D units in each case and arenot present in cumulated form in a domain-like manner, as shown by the29Si NMR spectroscopy, especially in the shift region of the Tstructures.

Gas chromatography analysis shows that, typically, simple siloxanecycles such as D₄ (octamethylcyclotetrasiloxane), D₅(decamethylcyclopentasiloxane) and D₆ (dodecamethylcyclohexasiloxane)are present in the equilibrates only in proportions by weight of lessthan 10%.

If desired for the respective later application (for example within thescope of the VOC discussion (VOC=volatile organic compounds) or ofanti-fogging), these siloxane cycles can be removed by simpledistillation and recycled.

On the other hand, the thermal reaction conditions chosen in the contextof the inventive process can be called extremely moderate, compared tothe temperatures of up to 600° C. described in the literature.

The cyclic branched siloxanes of the D/T type are obtained in virtuallyquantitative yields, based in each case on trialkoxysilane used.

It will be immediately apparent to the person skilled in the art thatthe branched organomodified siloxanes obtained by acidic equilibrationfrom the second step are suitable as starting material for production ofstabilizers for PUR foams, for production of defoamers, for productionof paint additives, for production of emulsifiers, especially ofcosmetic emulsifiers, for production of cosmetic conditioners, forproduction of deaerating agents, for production of demulsifiers, forproduction of textile finishes, for production of building protectionadditives, for production of polymer additives, especially anti-scratchadditives, for production of antifouling additives or coatings, and forproduction of anti-icing coatings. This use forms a further part of thesubject-matter of the present invention.

Depending on the functionality incorporated in the second step (e.g. SiHgroup (see Example 6) or SiCl group (see Example 10)), for all theseaforementioned applications, after selection of appropriateco-reactants, SiC-bonded final products are obtainable viahydrosilylation, or else SiOC-bonded final products are obtainable viadehydrogenative SiOC bond formation or condensation by the known methodsof silicon chemistry.

The ²⁹Si NMR samples, in the context of this invention, are analyzed ata measurement frequency of 79.49 MHz in a Bruker Avance III spectrometerequipped with a 287430 sample head with gap width 10 mm, dissolved at22° C. in CDCl₃ and against tetramethylsilane (TMS) as external standard[δ(²⁹Si)=0.0 ppm].

The weight-average molar mass M_(w) and the molar mass distributionM_(w)M_(n) are determined in the context of this invention using anEcoSEC GPC/SEC instrument from TOSOH Bioscience GmbH by gel permeationchromatography from toluenic solutions of the siloxanes. A Micro SDV1000/10000 column of length 55.00 cm is used, combined with an EcoSEC RIdetector (dual flow refractive index detection). The polystyrenestandard covers the molar mass range from 162 g/mol to 2 520 000 g/mol.

EXAMPLES

1) Preparation of a Cyclic Branched Siloxane Having a Target D/T Ratioof 8:1 (Inventive)

In a 500 ml four-neck round-bottom flask with a precision glass stirrerand a reflux condenser on top, 40.5 g (0.227 mol) ofmethyltriethoxysilane are heated to 60° C. together with 134.5 g (0.363mol) of decamethylcyclopentasiloxane in 200 ml of toluene whilestirring, 0.375 g of trifluoromethanesulfonic acid is added and themixture is equilibrated for 4 hours. Then 12.3 g of water and 3.1 g ofethanol are added and the mixture is heated to reflux temperature atabout 80° C. for a further 4 hours. The reflux condenser is exchangedfor a distillation system, and the constituents that are volatile up to100° C. are distilled off within the next hour. Then the distillationsystem is replaced by the reflux condenser, 6.15 g of water and 1.5 g ofethanol are added to the mixture and the mixture is left to boil for afurther hour. The reflux condenser is then replaced once again by adistillation system, and the constituents that are volatile up to 100°C. are removed over the course of the next hour. The mixture is cooledto 60° C. and then 4 m % of sodium hydrogencarbonate is added, themixture is stirred for half an hour, then the salt is separated from theliquid phase with the aid of a fluted filter. The volatiles aredistilled off at 70° C. and a pressure of <1 mbar on a rotaryevaporator, and a colorless mobile liquid is isolated, the ²⁹Si NMRspectrum of which indicates a D/T ratio of 7.62:1 (target: 8:1).

The GPC has a broad molar mass distribution, characterized byM_(w)=70317 g/mol; M_(n): 1941 g/mol and M_(w)/M_(n)=36.24.

2) Preparation of a Cyclic Branched Siloxane Having a Target D/T Ratioof 6:1 (Inventive)

Analogously to Example 1, in a 500 ml four-neck round-bottom flask witha precision glass stirrer and a reflux condenser on top, 52.2 g (0.293mol) of methyltriethoxysilane are heated to 60° C. together with 130.3 g(0.351 mol) of decamethylcyclopentasiloxane in 200 ml of toluene whilestirring, 0.400 g of trifluoromethanesulfonic acid is added and themixture is equilibrated for 4 hours. Then 15.8 g of water and 4.0 g ofethanol are added and the mixture is heated to reflux temperature atabout 80° C. for a further 4 hours. The reflux condenser is exchangedfor a distillation system, and the constituents that are volatile up to100° C. are distilled off within the next hour. Then the distillationsystem is replaced by a reflux condenser, 7.90 g of water and 2.0 g ofethanol are added to the mixture and the mixture is left to boil for afurther hour. The reflux condenser is then replaced once again by adistillation system, and the constituents that are volatile up to 100°C. are removed over the course of the next hour. The mixture is cooledto 60° C. and then 4 m % of sodium hydrogencarbonate is added, themixture is stirred for half an hour, then the salt is separated from theliquid phase with the aid of a fluted filter. The volatiles aredistilled off at 70° C. and a pressure of <1 mbar on a rotaryevaporator, and a colorless mobile liquid is isolated, the ²⁹Si NMRspectrum of which indicates a D/T ratio of 5.85:1 (target: 6:1).

3) Preparation of a Greater Amount of a Cyclic Branched Siloxane Havinga Target D/T Ratio of 6:1 (Inventive)

In a 4000 ml four-neck round-bottom flask with a precision glass stirrerand a reflux condenser on top, 261.0 g (1.46 mol) ofmethyltriethoxysilane are heated to 60° C. together with 652.5 g (1.76mol) of decamethylcyclopentasiloxane and 200 ml of toluene whilestirring, 1.983 g of trifluoromethanesulfonic acid is added and themixture is equilibrated for 4 hours. Then 79.0 g of water and 19.75 g ofethanol are added and the mixture is heated to reflux temperature atabout 80° C. for a further 4 hours. The reflux condenser is exchangedfor a distillation system, and the constituents that are volatile up to100° C. are distilled off within the next hour. Then the distillationsystem is replaced by a reflux condenser, 26.30 g of water and 6.6 g ofethanol are added to the mixture and the mixture is left to boil for afurther hour. The reflux condenser is then replaced once again by adistillation system, and the constituents that are volatile up to 100°C. are removed over the course of the next hour. The mixture is cooledto 60° C. and then 4 m % of sodium hydrogencarbonate is added, themixture is stirred for half an hour, then the salt is separated from theliquid phase with the aid of a fluted filter. The volatiles aredistilled off at 70° C. and a pressure of <1 mbar on a rotaryevaporator, and a colorless mobile liquid is isolated, the corresponding²⁹Si NMR spectrum of which indicates a D/T ratio of 5.74:1 (target:6:1). The dynamic viscosity is 598 mPas at 25° C. The GC shows residualcontents of D₄=3.2%, D₅=3.9% and D₆=1.4%.

The GPC has a broad molar mass distribution, characterized byM_(w)=91965 g/mol; Mn: 2214 g/mol and M_(w)/M_(n)=41.54.

4) Preparation of a Cyclic Branched Siloxane Having a Target D/T Ratioof 4:1 (Unadjusted Amount of Solvent)

Analogously to Example 1, in a 500 ml four-neck round-bottom flask witha precision glass stirrer and a reflux condenser on top, 73.5 g (0.412mol) of methyltriethoxysilane are heated to 60° C. together with 122.3 g(0.33 mol) of decamethylcyclopentasiloxane in 220 ml of toluene whilestirring, 0.436 g of trifluoromethanesulfonic acid is added and themixture is equilibrated for 4 hours. Then 22.3 g of water and 5.6 g ofethanol are added and the mixture is heated to reflux temperature atabout 80° C. for a further 4 hours. The reflux condenser is exchangedfor a distillation system, and the constituents that are volatile up to100° C. are distilled off within the next hour. Then the distillationsystem is replaced by a reflux condenser, 7.50 g of water and 1.9 g ofethanol are added to the mixture and the mixture is left to boil for afurther hour. The reflux condenser is then replaced once again by adistillation system. In the course of the subsequent distillation, theviscosity of the bottoms rises so significantly that the mass ofsilicone gelates and is discarded.

5) Preparation of a Cyclic Branched Siloxane Having a Target D/T Ratioof 4:1 (Inventive, Adjusted Amount of Solvent of 1:3)

Analogously to Example 1, in a 500 ml four-neck round-bottom flask witha precision glass stirrer and a reflux condenser on top, 36.8 g (0.206mol) of methyltriethoxysilane are heated to 60° C. together with 61.2 g(0.165 mol) of decamethylcyclopentasiloxane in 330 ml of toluene whilestirring, 0.218 g of trifluoromethanesulfonic acid is added and themixture is equilibrated for 4 hours. Then 11.2 g of water and 2.8 g ofethanol are added and the mixture is heated to reflux temperature atabout 80° C. for a further 4 hours. The reflux condenser is exchangedfor a distillation system, and the constituents that are volatile up to100° C. are distilled off within the next hour. Then the distillationsystem is replaced by a reflux condenser, 2.70 g of water and 0.9 g ofethanol are added to the mixture and the mixture is left to boil for afurther hour. The reflux condenser is then replaced once again by adistillation system, and the constituents that are volatile up to 100°C. are removed over the course of the next hour. The mixture is cooledto 60° C. and then 4 m % of sodium hydrogencarbonate is added, themixture is stirred for half an hour, then the salt is separated from theliquid phase with the aid of a fluted filter. The volatiles aredistilled off at 70° C. and a pressure of <1 mbar on a rotaryevaporator, and a colorless mobile liquid is isolated, the ²⁹Si NMRspectrum of which indicates a D/T ratio of 3.6:1 (target: 4:1).

The GPC has a molar mass distribution characterized by M_(w)=12344g/mol; M_(n):3245 g/mol and M_(w)/M_(n)=2.63.

6) Preparation of a Branched Hydrosiloxane Having Terminal SiH Functionsfrom the Cyclic Branched Siloxane Prepared in Example 1 withα,ω-dihydropolydimethylsiloxane and decamethylcyclopentasiloxane

37.4 g of the cyclic branched siloxane prepared in Example 1 are heatedto 40° C. together with 6.3 g of an α,ω-dihydropolydimethylsiloxane (SiHvalue: 2.90 eq/kg) and 186.3 g of decamethylcyclopentasiloxane withaddition of 0.25 g of trifluoromethanesulfonic acid (0.1 m % based onthe overall mixture) in a 500 ml four-neck flask with precision glassstirrer and a reflux condenser on top for 6 hours, then 5 g of sodiumhydrogencarbonate were added and the mixture was stirred for a further30 minutes. With the aid of a filter press (Seitz K 300 filter disc),the salt was separated from the equilibrate.

What is obtained is a colorless branched hydrosiloxane havingdimethylhydrosiloxy functions in its termini (SiH value: 0.30 eq/kg).The corresponding ²⁹Si NMR spectrum confirms the target structure.

7) Preparation of a Branched Siloxane Having Terminal Ethoxy Functions(Inventive)

114.8 g of the cyclic branched siloxane prepared in Example 2 are heatedto 60° C. together with 33.9 g of dimethyldiethoxysilane and 101.1 g ofdecamethylcyclopentasiloxane with addition of 0.25 g oftrifluoromethanesulfonic acid (0.1 m % based on the overall mixture) ina 500 ml four-neck flask with precision glass stirrer and a refluxcondenser on top for 6 hours, then 5 g of sodium hydrogencarbonate wereadded and the mixture was stirred for a further 30 minutes. With the aidof a filter press (Seitz K 300 filter disc), the salt was separated fromthe equilibrate.

The corresponding ²⁹Si NMR spectrum confirms the target structure.

8) Preparation of a Branched Siloxane Having Terminal Vinyl Functions(Inventive)

109.2 g of the cyclic branched siloxane prepared in Example 3 are heatedto 60° C. together with 41.3 g of divinyltetramethyldisiloxane and 99.5g of decamethylcyclopentasiloxane with addition of 0.25 g oftrifluoromethanesulfonic acid (0.1 m % based on the overall mixture) ina 500 ml four-neck flask with precision glass stirrer and a refluxcondenser on top for 6 hours, then 5 g of sodium hydrogencarbonate wereadded and the mixture was stirred for a further 30 minutes. With the aidof a filter press (Seitz K 300 filter disc), the salt was separated fromthe equilibrate.

The corresponding 29Si NMR spectrum confirms, as the target structure, abranched siloxane bearing terminal vinyl functions.

9) Preparation of a Branched Silicone Oil (Inventive)

111.6 g of the cyclic branched siloxane prepared in Example 3 are heatedto 60° C. together with 36.7 g of hexamethyldisiloxane and 101.7 g ofdecamethylcyclopentasiloxane with addition of 0.25 g oftrifluoromethanesulfonic acid (0.1 m % based on the overall mixture) ina 500 ml four-neck flask with precision glass stirrer and a refluxcondenser on top for 6 hours, then 5 g of sodium hydrogencarbonate wereadded and the mixture was stirred for a further 30 minutes. With the aidof a filter press (Seitz K 300 filter disc), the salt was separated fromthe equilibrate.

The corresponding 29Si NMR spectrum confirms, as the target structure, abranched non-functional silicone oil.

10) Preparation of a Branched Sulfato-Bridged Siloxane Having TerminalChlorine Functions (Chlorosiloxanyl Sulfate, Inventive)

a) Preparation of a Linear Chlorosiloxanyl Sulfate Precursor

A 500 ml four-neck flask with precision glass stirrer and internalthermometer and with a reflux condenser on top is initially charged with105.4 g of an α,ω-dichloropolydimethylsiloxane of mean chain lengthN=5.5 together with 28.2 g of decamethylcyclopentasiloxane whilestirring, and 5.6 g of concentrated sulfuric acid are added. The mixtureis left to reactor at 50° C. for one hour and then at 100° C. for 2hours. After cooling to 20° C., a colorless clear liquid is obtained.

b) Equilibration of the Precursor Having D/T Cycles Obtained in a)

110.8 g of a D/T siloxane prepared in analogy to Example 2 with a D/Tratio determined by ²⁹Si NMR spectroscopy of 5.63:1 are added to theprecursor obtained in a) while stirring within 5 minutes.

The equilibration is effected with vigorous stirring of the reactants at22° C. for 30 minutes, then at 50° C. for 1 hour and at 100° C. for 6hours.

With application of an auxiliary vacuum of 1 mbar, volatile constituentsare removed at 50° C. over a period of 2 hours. After the liquid phasehas been cooled, a water-clear colorless liquid having an acid value of1.82 mmol of acid/g of substance (theoretically: 1.853 mmol of acid/g ofsubstance) is isolated. ²⁹Si NMR spectroscopy confirms the desiredstructure.

The invention claimed is:
 1. A mixture of cyclic branched siloxaneshaving exclusively D and T units and having no functional groups,wherein the cumulative proportion of the D and T units having Si-alkoxyand/or SiOH groups that are present in the siloxane matrix isdeterminable by ²⁹Si NMR spectroscopy, is ≤2 mole percent, based on thetotality of silicon detected by spectroscopy.
 2. The mixture of cyclicbranched siloxanes having exclusively D and T units according to claim1, wherein the branching T unit derives from alkyltrialkoxysilanesand/or phenyltrialkoxysilanes.
 3. The mixture of cyclic branchedsiloxanes having exclusively D and T units according to claim 2, whereinthe molar mass ratio of the mixture Mw/Mn is in the range of 2<Mw/Mn<50.4. The mixture of cyclic branched siloxanes having exclusively D and Tunits according to claim 1, wherein the branching T unit derives frommethyltriethoxysilane.
 5. The mixture of cyclic branched siloxaneshaving exclusively D and T units according to claim 4, wherein the molarmass ratio of the mixture Mw/Mn is in the range of 2<Mw/Mn<50.
 6. Themixture of cyclic branched siloxanes having exclusively D and T unitsaccording to claim 1, wherein the ratio of D to T units is between 6:1and 4:1.
 7. The mixture of cyclic branched siloxanes having exclusivelyD and T units according to claim 6, wherein the molar mass ratio of themixture Mw/Mn is in the range of 2<Mw/Mn<50.
 8. A mixture of cyclicbranched siloxanes having exclusively D and T units and having nofunctional groups, wherein the cumulative proportion of the D and Tunits having Si-alkoxy and/or SiOH groups that are present in thesiloxane matrix; determinable by ²⁹Si NMR spectroscopy, is ≤2 molepercent, wherein the ratio of D to T units is between 10:1 and 3:1. 9.The mixture of cyclic branched siloxanes having exclusively D and Tunits according to claim 8, wherein the molar mass ratio of the mixtureMw/Mn is in the range of 2<Mw/Mn<50.
 10. The mixture of cyclic branchedsiloxanes having exclusively D and T units according to claim 8, whereinthe molar mass ratio of the mixture Mw/Mn is in the range of 2<Mw/Mn<50.